Dryer added fabric softening articles are a convenient way of softening fabrics. More convenient than single use articles, such as fabric softening dryer sheets, are multiple use articles, which are placed and kept inside the dryer for a multitude of drying cycles, releasing fabric softener to successive loads of the dryer.
Multiple use dryer added fabric softening articles comprising a quaternary ammonium salt fabric softener and a high melting carrier, such as an ethylenediamine fatty acid diamide, are known from U.S. 2003/0195130, U.S. 2004/0167056 and U.S. 2006/0277689. The dryer added fabric softening articles disclosed in these documents are made by melting and mixing the fabric softener and the carrier and solidifying the melt in the desired shape by methods such as injection molding or casting, as described in U.S. 2004/0167056 paragraph [0062]. One problem associated with dryer added fabric softening articles made this way is the staining of dark fabrics in the first cycles of using the article by excessive amounts of fabric softener, which can be traced back to an insufficient initial surface hardness of the article as discussed in U.S. 2006/0277689 paragraph [0028] and demonstrated in U.S. 2004/0167056 FIG. 6.
U.S. 2006/0277689 proposes to add from 5 to 30% by weight of an elasticity, shrinkage or surface hardness additive, but provides no teaching on which additive could provide an improved surface hardness. The only related example 3 shows a lowering of the surface hardness by the additive of sample 1.
U.S. 2007/0066510 teaches to use a fabric softener active consisting essentially of an ester quaternary ammonium compound free of any other quaternary ammonium compound to reduce the staining of dark fabrics. However, nothing is taught on how to obtain a high initial surface hardness for a dryer added fabric softening article comprising such an ester quaternary ammonium compound.
R. H. Pryce-Jones et al., J. Am. Oil Chem. Soc. 73 (1996) 311 to 319 discloses the results of DSC measurements on ethylenediamine fatty acid diamides. Materials crystallized from solution showed an endothermal solid phase transition at temperatures of 98 to 127° C. with a transition enthalpy of more than 30 J/g, but no exothermal solid phase transition. Endothermal solid phase transitions with a similar transition enthalpy were not observed for materials obtained by solidifying the melt during DSC at a rate of 10° C./min. The document contains no teachings on mixtures containing ethylenediamine fatty acid diamides and a fabric softener and the surface hardness of such mixtures.
There remains a need of providing a fabric softening composition that can be shaped to a dryer added fabric softening article having a high initial surface hardness.